This invention relates to wireless devices, and more particularly, to an antenna attached to a remote sensing apparatus or interrogator for use in detecting wireless communications devices such as radio frequency identification (RFID) tags or transponders affixed to livestock for identification of an animal as it passes proximate to the antenna.
Wireless communications devices, including wireless memory devices for storing and transmitting data such as RFID transponders or tags are generally known in the art. Such transponders are particularly used in the livestock industry for such uses as tracking and accounting for animals being shipped and, for distinguishing between animals, such as upon introduction to a herd or feedlot. The devices are also useful in tracking, such as used in connection with salmon and other fish for scientific and environmental purposes.
However, difficulties have existed for some time with electronically reading identification tags mounted on livestock or fish. First, the transponder to be monitored is passive and is typically implanted within the fish or animals where the final position or orientation of the implanted transponder cannot be controlled. Alternatively, the transponder is externally affixed to an animal""s ear, such as with livestock, and the orientation of the transponder varies with the movement of the animal""s head. In this regard, to optimize reading of a transponder, the transponder antenna should be properly aligned with the fields generated by the interrogator antenna. Also, environmental conditions need to be considered that could adversely affect orientation of the transponder relative to the antenna, such as water currents in the case of fish, or rain, wind and sun in the case of outdoor livestock. Further, for optimum activation and communication, an adequate electromagnetic field must be generated by the interrogation device or interrogation antenna. Thus, weak magnetic interrogation fields and/or poorly orientated transponders can inhibit accurate interrogation of a transponder.
In the early prior art, these problems were addressed by utilizing a hand-held interrogator to read a transponder affixed to an animal. In this way, the reader could be positioned closely adjacent the animal to guarantee a sufficiently strong electromagnetic excitation field proximate the transponder. It also allowed the reader to be moved or swept over the animal to accommodate different transponder orientation. However, the cost in terms of wages and worker safety matters associated with dedicating a worker to the identification effort has provided motivation to attempt to automate the process. As a result, various types of automated identification devices have been developed.
More recently prior art interrogators for livestock identification have been directed to antenna arrangements rigidly mounted on a cattle gate or similar walkthrough. Such systems generally provide single or multiple antennas, typically placed on the sides, top and in some instances along the bottom of a walkthrough or chute in order to increase the area of magnetic field coverage for detecting a transponder tag attached to an animal.
These prior art systems present a problem in manufacturing, as well as transportation of the antenna, because of size and installation requirements. Such antennas are generally mounted inside panels for rigidity. Moreover, the panels may, in turn, be rigidly mounted in a larger structure, such as a walkthrough or chute to facilitate use with herds and other large groups of animals. However, because of the enclosed nature of the walkthroughs, the antenna structures or panels may present an obstacle and interfere with the cattle or other livestock passing through the walkthrough. Additionally, because of physical size and complexity, the walkthrough antennas are generally erected in a single or permanent location, typically in conjunction with a loading chute. As a result, the livestock must be brought to the interrogator rather than bringing the interrogator to where the animals are located. This can become a logistical and practical nightmare with large herds such as in feedlots where different groups are spread over large areas.
Nevertheless, the prior art antenna systems using such single or multiple antennas generally failed to provide full field coverage to accurately read the transponder information. As a result, prior art antenna arrangements may incorporate up to four loop antennas, arranged along the sides, top and the bottom of the walkthrough. However, even the use of up to four of the loop antennas often did not provide adequate coverage due to interference between the electromagnetic fields of the various loop antennas.
It would therefore be advantageous for an antenna to be developed which would alleviate the above-identified shortcomings of the prior art and otherwise improve the ability to accurately read transponders at varied orientations.
The present invention addresses the problems of the prior art in a flexible interrogator antenna design having a single antenna with an inner and an outer antenna coil positioned in a flexible, rectangular arrangement and providing multi-directional electromagnetic field generation capability.
In one embodiment, the antenna is disposed within a flexible mat or housing allowing it to be positioned in a configuration having two sides and a top, easily positioned across a temporary frame to form a walkthrough corridor or chute through which livestock having an attached transponder can be driven. When thus formed, a multi-directional field is generated within the walkthrough. In particular, the antenna of the present invention provides an electromagnetic field generally in each of three mutually perpendicular directions. For illustrative purposes, the three fields can be viewed as having an xe2x80x98Xxe2x80x99, xe2x80x98Yxe2x80x99 and xe2x80x98Zxe2x80x99 axis, respectively, with the xe2x80x98Zxe2x80x99 axis along the direction of passage through the walkthrough.
The electromagnetic fields created by the outer antenna coil would normally be in phase. However, in bending the antenna to form the walkthrough, the fields generated by the outer coils in the side walls become out of phase, creating an electromagnetic field within the walkthrough along the xe2x80x98Zxe2x80x99 axis with a cancelling or null zone along the center. The effects of the null zone can be minimized by changing the size and shape of the coils to thereby move the null zone to different locations where it will have less effect given the relative location of the transponder as they traverse the passageway. The electromagnetic fields created by both antenna coils in the top portion are in phase and create fields along the xe2x80x98Yxe2x80x99 axis. The electromagnetic fields created by the inner coils in both side walls and the outer coil in the left sidewall with respect to the direction of passage create fields in the xe2x80x98Xxe2x80x99 direction. Thus, as hereinafter described, the detection of a transponder passing through the walkthrough will be enhanced by the multidirectional electromagnetic fields of the antenna, no matter what the orientation of the transponder.
Thus, if the transponder passes through the walkthrough with its coil antenna oriented parallel to the ground, it will be optimally read by the electromagnetic field created in the xe2x80x98Yxe2x80x99 direction by the coils along the top of the walkthrough. If the transponder passes through the walkthrough with its coil antenna in a vertical/sideways orientation, it will be optimally read by the electromagnetic field created in the xe2x80x98Xxe2x80x99 direction by the inner coils on both sides and the outer coil on the left side of the walkthrough. If the transponder passes through the walkthrough with its coil antenna in a vertical orientation, perpendicular to the xe2x80x98Zxe2x80x99 axis, it will be optimally read by the electromagnetic field created by the outer coils in both side walls of the walkthrough. No matter what the orientation is of the transponder antenna in passing through the walkthrough, the likelihood of it being successfully read will be enhanced by the above described multidirectional electromagnetic fields acting in concert. In fact, the multidirectional fields thus generated eliminate the need for an additional antenna in the floor of the walkthrough, simplifying manufacture and reducing cost.
The flexible design further allows for easy transportation of the antenna, as the flexible arrangement can be rolled up, readily transported to a desired site, e.g., where the animals are located, and then mounted on a simple and/or temporary frame at the site. The antenna can also be easily utilized in conjunction with existing loading chutes.
Accordingly, it is an object of the invention to provide an improved transponder interrogator antenna for use with a remote sensing apparatus and which has multi-directional electromagnetic field generation capability.
It is another object of the invention to provide an antenna capable of detecting a transponder irrespective of the orientation of the transponder passing through the electromagnetic fields generated by the antenna.
Still another object of the invention is to provide a flexible antenna having multi-directional electromagnetic field generation capability that is capable of being easily transported to a remote site, and installed on an existing loading chute or on a frame that can be readily erected at the remote site.
Other objects and features of the present invention will become apparent from the following detailed description in conjunction with the accompanying drawing figures. It is to be understood, however, that the drawings, which are not to scale, are designed solely for the purpose of illustration and not as definition of the limits of the invention, for which reference should be made to the appended claims.